The major objective is to make a comprehensive study of Marek's disease herpesvirus induced transient paralysis in chickens by investigating the immunologic, pathologic, viral and genetic factors associated with the disorder. The previous finding that susceptibility to transient paralysis is determined by major histocompatibility complex (MHC) genes, allows for a meaningful analysis of crucial differences between genetically susceptible and genetically resistant animals. The specific aims are to determine: (a) the most likely site or sites of the nervous system that are affected as indicated by ante mortem neurological examination and clinical laboratory tests; (b) the definitive lesion or lesions that characterize transient paralysis as determined by light and electron microscopic examination of tissues from transient paralysis resistant and susceptible birds; (c) the immunopathologic nature of the disease with particular emphasis on the relevance of genetically controlled immune responsiveness, autoimmunity and formation of immune complexes; (d) the factors associated with the variability of different strains of Marek's disease virus to cause transient paralysis; and (e) the comparative effects of different MHC haplotypes that determine susceptibility to the disease. Procedures to be used include electroencephalography, electromyography, serum enzyme and cerebrospinal fluid analysis and histopathologic examinations. Anti-viral immune responses will be studied by in vitro virus neutralization assays. Importance of humoral and cellular immunity of resistant and susceptible chickens will be examined by using bursectomized and thymectomized chickens. Fluorescent antibody techniques will be utilized for exploring immune complex formation and tissue distribution of virus.